@@ -424,6 +424,16 @@ The value is measured in bytes. The default is @samp{41943040}
(fourty mibibytes).
@end deftp
+@deftp Tunable glibc.pthread.rseq
+The @code{glibc.pthread.rseq} tunable can be set to @samp{0}, to disable
+restartable sequences support in @theglibc{}. This enables applications
+to perform direct restartable sequence registration with the kernel.
+The default is @samp{1}, which means that @theglibc{} performs
+registration on behalf of the application.
+
+Restartable sequences are a Linux-specific extension.
+@end deftp
+
@node Hardware Capability Tunables
@section Hardware Capability Tunables
@cindex hardware capability tunables
@@ -368,7 +368,10 @@ start_thread (void *arg)
__ctype_init ();
/* Register rseq TLS to the kernel. */
- rseq_register_current_thread (pd);
+ {
+ bool do_rseq = THREAD_GETMEM (pd, flags) & ATTR_FLAG_DO_RSEQ;
+ rseq_register_current_thread (pd, do_rseq);
+ }
#ifndef __ASSUME_SET_ROBUST_LIST
if (__nptl_set_robust_list_avail)
@@ -677,6 +680,11 @@ __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
pd->flags = ((iattr->flags & ~(ATTR_FLAG_SCHED_SET | ATTR_FLAG_POLICY_SET))
| (self->flags & (ATTR_FLAG_SCHED_SET | ATTR_FLAG_POLICY_SET)));
+ /* Inherit rseq registration state. Without seccomp filters, rseq
+ registration will either always fail or always succeed. */
+ if ((int) THREAD_GETMEM (self, rseq_area.cpu_id) >= 0)
+ pd->flags |= ATTR_FLAG_DO_RSEQ;
+
/* Initialize the field for the ID of the thread which is waiting
for us. This is a self-reference in case the thread is created
detached. */
@@ -23,6 +23,9 @@
#include <tls.h>
#include <rseq-internal.h>
+#define TUNABLE_NAMESPACE pthread
+#include <dl-tunables.h>
+
#ifndef __ASSUME_SET_ROBUST_LIST
bool __nptl_set_robust_list_avail;
rtld_hidden_data_def (__nptl_set_robust_list_avail)
@@ -92,7 +95,13 @@ __tls_init_tp (void)
}
}
- rseq_register_current_thread (pd);
+ {
+ bool do_rseq = true;
+#if HAVE_TUNABLES
+ do_rseq = TUNABLE_GET (rseq, int, NULL);
+#endif
+ rseq_register_current_thread (pd, do_rseq);
+ }
/* Set initial thread's stack block from 0 up to __libc_stack_end.
It will be bigger than it actually is, but for unwind.c/pt-longjmp.c
@@ -27,5 +27,11 @@ glibc {
type: SIZE_T
default: 41943040
}
+ rseq {
+ type: INT_32
+ minval: 0
+ maxval: 1
+ default: 1
+ }
}
}
@@ -48,6 +48,7 @@ struct pthread_attr
#define ATTR_FLAG_OLDATTR 0x0010
#define ATTR_FLAG_SCHED_SET 0x0020
#define ATTR_FLAG_POLICY_SET 0x0040
+#define ATTR_FLAG_DO_RSEQ 0x0080
/* Used to allocate a pthread_attr_t object which is also accessed
internally. */
@@ -136,6 +136,12 @@ tests-internal += \
tst-sigcontext-get_pc \
# tests-internal
+ifneq (no,$(have-tunables))
+tests-internal += \
+ tst-rseq-disable \
+ # tests-internal $(have-tunables)
+endif
+
tests-time64 += \
tst-adjtimex-time64 \
tst-clock_adjtime-time64 \
@@ -227,6 +233,8 @@ $(objpfx)tst-mman-consts.out: ../sysdeps/unix/sysv/linux/tst-mman-consts.py
< /dev/null > $@ 2>&1; $(evaluate-test)
$(objpfx)tst-mman-consts.out: $(sysdeps-linux-python-deps)
+tst-rseq-disable-ENV = GLIBC_TUNABLES=glibc.pthread.rseq=0
+
endif # $(subdir) == misc
ifeq ($(subdir),time)
@@ -21,22 +21,27 @@
#include <sysdep.h>
#include <errno.h>
#include <kernel-features.h>
+#include <stdbool.h>
#include <stdio.h>
#include <sys/rseq.h>
#ifdef RSEQ_SIG
static inline void
-rseq_register_current_thread (struct pthread *self)
+rseq_register_current_thread (struct pthread *self, bool do_rseq)
{
- int ret = INTERNAL_SYSCALL_CALL (rseq,
- &self->rseq_area, sizeof (self->rseq_area),
- 0, RSEQ_SIG);
- if (INTERNAL_SYSCALL_ERROR_P (ret))
- THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+ if (do_rseq)
+ {
+ int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
+ sizeof (self->rseq_area),
+ 0, RSEQ_SIG);
+ if (!INTERNAL_SYSCALL_ERROR_P (ret))
+ return;
+ }
+ THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
}
#else /* RSEQ_SIG */
static inline void
-rseq_register_current_thread (struct pthread *self)
+rseq_register_current_thread (struct pthread *self, bool do_rseq)
{
THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
}
new file mode 100644
@@ -0,0 +1,89 @@
+/* Test disabling of rseq registration via tunable.
+ Copyright (C) 2021 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#include <errno.h>
+#include <stdio.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/xthread.h>
+#include <sysdep.h>
+#include <unistd.h>
+
+#ifdef RSEQ_SIG
+
+/* Check that rseq can be registered and has not been taken by glibc. */
+static void
+check_rseq_disabled (void)
+{
+ struct pthread *pd = THREAD_SELF;
+ TEST_COMPARE ((int) pd->rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+
+ int ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
+ 0, RSEQ_SIG);
+ if (ret == 0)
+ {
+ ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
+ RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+ TEST_COMPARE (ret, 0);
+ pd->rseq_area.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+ }
+ else
+ {
+ TEST_VERIFY (errno != -EINVAL);
+ TEST_VERIFY (errno != -EBUSY);
+ }
+}
+
+static void *
+thread_func (void *ignored)
+{
+ check_rseq_disabled ();
+ return NULL;
+}
+
+static void
+proc_func (void *ignored)
+{
+ check_rseq_disabled ();
+}
+
+static int
+do_test (void)
+{
+ puts ("info: checking main thread");
+ check_rseq_disabled ();
+
+ puts ("info: checking main thread (2)");
+ check_rseq_disabled ();
+
+ puts ("info: checking new thread");
+ xpthread_join (xpthread_create (NULL, thread_func, NULL));
+
+ puts ("info: checking subprocess");
+ support_isolate_in_subprocess (proc_func, NULL);
+
+ return 0;
+}
+#else /* !RSEQ_SIG */
+static int
+do_test (void)
+{
+ FAIL_UNSUPPORTED ("glibc does not define RSEQ_SIG, skipping test");
+}
+#endif
+
+#include <support/test-driver.c>